The present invention relates to an optical characteristic measuring apparatus for precisely measuring optical characteristics of an eye to be examined by projecting a specific pattern on the retina of the eye, and particularly to an optical characteristic measuring apparatus capable of measuring optical characteristics of an irregular astigmatism component of the eye.
A prior art apparatus for measuring optical characteristics of an eye to be examined, known as a refractometer, is capable of expressing the optical characteristics of the eye merely as a spherical component, a regular astigmatism component and the angle of the axis of the regular astigmatism component. Some eyes have an irregular astigmatism component in addition to a regular astigmatism component. If the quantity of the irregular astigmatism component is large, such an irregular astigmatism may be required to be corrected by use of a set of contact lenses instead of a pair of spectacles or through examination of the eye by a medical doctor.
While the present applicant has developed an optical characteristic measuring apparatus with consideration given to the irregular astigmatism component and filed the patent application thereof, such an apparatus has a problem that if an eye to be examined is not in emmetropia, an index point cannot be projected as a point image on the eyeground of the eye by the effect of the astigmatism component or the like, tending to cause a measurement error.
In view of the foregoing, it has been strongly needed to develop an optical characteristic measuring apparatus capable of forming a specific pattern on the retina of an eye to be examined even if the eye has regular and irregular astigmatism components.